Influence of solid/liquid interfaces on the microstructure and stress-rupture life of the single-crystal nickel-base superalloy NASAIR 100

Abstract

The [001] oriented single crystals of nickel-base superalloy NASAIR 100 with the planar, cellular, coarse-dendritic, and fine-dendritic solid/liquid (S/L) interfaces were prepared, respectively, and their microstructure and stress-rupture behavior at 1050 ЊC were investigated in both as-cast and solution heat-treated conditions. It was found that in as-cast single crystals of NASAIR 100, microsegregation and ␥/␥' eutectic produced in the solidification process increased, ␥' size decreased, and ␥' shape tended progressively to be cuboidal, with the successive transition of the S/L interface from planar to cellular, then to coarse-dendritic, and finally to fine-dendritic morphology. Furthermore, the solution temperature required to dissolve all as-cast ␥ ' and most of the ␥/␥' eutectic increased with the aforementioned successive transition of S/L interfaces. The reprecipitated ␥', after solution heat treatment (SHT), was usually fine and cuboidal. However, some W-rich phase was present in the heat-treated dendritic single crystals. Both the planar and the cellular single crystals of NASAIR 100 exhibited no superiority in stress-rupture life, irrespective of the heat-treatment conditions. Instead, the single crystals with dendritic morphology possessed excellent stress-rupture lives, after heat treatment at 1320 ЊC for 4 hours, followed by air cooling (AC). Perfect ␥ ' rafts with high-average aspect ratios formed during the stress-rupture tests of dendritic single crystals; in contrast, irregularly coarsening structures appeared in both the planar and cellular single crystals. The microstructure and solution behavior were illustrated in detail. Furthermore, the microstructural factors to affect the high-temperature stress-rupture life of the single crystals of NASAIR 100 were also analyzed.

Homogenizing a Nickel-Based Superalloy: Thermodynamic and Kinetic Simulation and Experimental Results

“…[5,6] Parameters for homogenization heat treatments for newly developed alloys are defined by trial and error, past practice on alloys of similar composition (parent alloys), or extensive experimental lab work. [2,3,6] If a sample of the cast microstructure can be obtained, the segregation across a dendrite arm can be profiled and the homogenization modeled with thermodynamic modeling software such as diffusion-controlled transformations (DICTRA).…”

Effect of orientation on the microstructure of nickel‐based crystalline superalloys

“…It was well known that the morphologies of γ′ were determined by the differential free energy (ΔG V ) and the differential strain energy (ΔG S ) for precipitating per unit volume of γ′ phase. As the cooling rate was low, the morphology of γ′ was mainly controlled by ΔG V and was cuboidal [11]. The shape of γ′ phase was spherical at high cooling rate.…”

“…The primary dendrite arm spacings control the microsegregation patterns and thus largely dictate the performance of the materials. It was established that the stages of nucleation and growth of γ′ precipitate were affected by the solute supersaturation [11]. The characteristics of the microstructure, for instance, coarse dendrite arm and serious interdendritic segregation could reduce the mechanical properties.…”

Deformed microstructure of the single-crystal superalloy NASAIR 100 at 1050 °C

“…In the cles in the four material conditions were cubic and evenly distributed, and the average edge lengths in the fine-dendritic specimen crept for 50 hours, one kind of vertical edge of single crystals were 0.56 m, i.e., larger than those in the criterion (where g is the diffraction vector), consistent with the observation in Reference 23. The dislocation configuraplanar and cellular single crystals (0.33 to 0.36 m), [21,22] the ␥ Ј rafts out of the necked zones in both the planar and tion was viewed under both two-beam and weak-beam darkfield conditions. cellular single crystals were thickened significantly and the lamellar morphologies were extremely imperfect, as shown Transmission electron microscopy revealed that after the 1300 ЊC for 4 hours and AC, heat treated cellular single in Figures 4(a) and (b).…”

“…So tively with the planar, cellular, coarse-dendritic, and finefar, the effect of such parameters as the testing temperatures, dendritic solid/liquid (S/L) interfaces. [21,22] The results the lattice misfit between ␥ and ␥ Ј phases, the external showed that the dendritic single crystals constantly posstress, and the size and shape of initial ␥ Ј precipitates on the sessed superior stress-rupture lives over both the planar and formation of ␥ Ј rafts has become clear. [10][11][12][13] For example, cellular single crystals, irrespective of the heat treatment Pollock and Argon [10] and Socrate and Parks [11] summarized conditions.…”